Lord Ganesha has the boon that he will be worshipped first in any auspicious occasion. During pooja all sorts of sacred flowers, fruits and sweets are allowed except Tulsi leaves. Though Tulsi is considered as very auspicious but due to involvement of curse it is prohibited to use tulsi leaves at the time of pooja. Once Lord Ganesha was engaged in deep meditation As Ganesha was doing pooja, there came Tulsi. The moment she saw Ganesha, she fell in love with him and requested him to take her as his wife.But Lord Ganesha had turned down the offer and said that he had no intention of marriage. This irritated Tulsi. She took it as her insult. In her fury she cursed Lord Ganesha saying that “you will certainly get married against you wishes”. On hearing this Lord Ganesha cursed her back in revenge saying,”You would be possessed by a demon in marriage, and then under a curse from the saints become a plant”. On hearing this curse, Tulsi felt sorry and prayed Ganesha. This pleased Lord Ganesha and he said, “Tulsi!, you will be regarded supreme among the plants. Whosoever worships the lord Vishnu with your leaves as offering would achieve liberation in heaven, but you will always be unacceptable by me. ” Later under Lord Ganesha's curse she became the wife of the demon king called Shankhachuda. She lived with him as his beloved wife, but then her husband was killed in a battle between Gods and demons and she turned into a plant of holy basil.Since Tulsi is dear to Lord Vishnu that is why Tulsi is held so sacred and grown into temples and houses offered in worship to Lord Vishnu.Also tulsi leaves are placed into the mouth of a dying person and when a Tulsi plant dies, it is immersed into a holy river, but it never offer to Lord Ganesha .